1. Field of the Invention
The present invention relates to a stereo camera. More particularly, the invention relates to a stereo camera which adjusts the distance between the optical axes of two photographing lenses being interlocked to the operation for adjusting the focal point.
2. Background of the Invention
In a stereo camera which takes two pieces of pictures at one time through a pair of right and left photographing lenses, the distance between the optical axes of the two photographing lenses has generally been fixed. In the stereo camera of this type in which the distance between the optical axes is fixed as shown in FIGS. 20(L) and 20(R) in an exaggerated manner, there develop non-overlapped regions (a-b, c-d) on the outer sides of the overlapped region (b-c) of the right and left photographed pictures L and R due to parallax of the two photographing lenses. As the distance to the subject becomes closer, furthermore, the position of the image of the subject in the right and left photographed pictures undergo a displacement toward the directions to approach each other.
The non-overlapped regions (a-b, c-d) are the portions where no stereo image is formed. When viewed by using a stereo slide viewer, the picture frames of the slide mount are overlapped on the boundaries of the non-overlapped regions as shown in FIG. 21, which is offensive to see. Besides, a stereo image of the subject at a distance closer than a focal distance appears in front of the stereo window (imaginary window in which the right and left picture frames of the mount become in agreement and appear as one picture when the stereo slide is viewed in a three-dimensional manner), which is unnatural. The stereo slides that have been proposed are accompanied by the above-mentioned defects.
In order to correct these defects, therefore, it has been attempted to mask the non-overlapped regions (a-b, c-d) of the right and left pictures by using a stereo slide mount having windows of a width narrower than the width of the pictures on the films, and to correct the perspective feeling by adjusting the pitch between the right and left films. The above method, however, is accompanied by a difficulty for determining a proper masking amount and for determining the positions of the films relative to the windows of the mount in the transverse direction and, besides, involves large loss of picture due to masking.
The above-mentioned problems caused by a difference in the visual field between the right and left photographing lenses can be solved by correcting the visual field by adjusting the distance between the optical axes of the right and left photographing lenses. As the devices for adjusting the distance between the optical axes of the stereo camera, there have been known the one of the manually adjusting type for adjusting the distance between the optical axes irrespective of the focal point-adjusting mechanism and the one of the automatically adjusting type for adjusting the distance between the optical axes being interlocked to a mechanism for adjusting the focal point. The device of the manually adjusting type is capable of adjusting the distance between the optical axes of the lenses to an optimum value depending upon a distance to the main subject and upon a distance between the main subject and another subject, but requires cumbersome operation for separately adjusting the focal point and the distance between the optical axes. Though scenery and still life can be photographed without interruption, this method lacks performance for quickly shooting pictures. Besides, the user may incorrectly set the distance between the optical axes unless he is well accustomed to the operation and function of the mechanism for adjusting the distance between the optical axes, which is never easy to handle. Accordingly, the automatic mechanism for adjusting the distance between the optical axes is more suited for a stereo camera used by general public than the manual mechanism for adjusting the distance between the optical axes.
The conventional automatic mechanism for adjusting the distance between the optical axes has been so constituted that the visual fields of the right and left photographing lenses are brought into agreement at all times at a focal distance and that the distance between the optical axes is automatically adjusted being interlocked to the adjustment of the focal point to obtain a constant effect for correcting the distance between the optical axes.
If it is presumed that the lens is a thin lens and, focal distance of the lens f
distance from the subject to a main point of the lens L
distance from the focal point of the lens to the image-forming position xcex94if
then,
xcex94if=f2/(Lxe2x88x92f)xe2x80x83xe2x80x83(1)
and the distance from the main point of the lens to the surface of the film is given by f+xcex94if.
FIG. 22 illustrates loci of motion of main points of the photographing lenses at the focal distance for bringing into agreement the visual fields of the right and left photographing lenses. When the pitch between the right and left exposed pictures of the stereo camera is denoted by P, the shifting amount Sl of the right and left lenses for bringing into agreement the visual fields of the right and left photographing lenses at the focal distance is given by,
Sl=(P/2)xc3x97(f+xcex94if)/(L+f+xcex94if)xe2x80x83xe2x80x83(2)
A table of FIG. 23 illustrates relationships between the delivering amounts xcex94if of the lenses in the direction of the optical axes and the shifting amounts Sl in the direction at right angles with the optical axes based upon the above-mentioned formula when a focal distance of the lenses is 36 mm and the pitch P between the right and left exposed pictures is 66 mm. When the right and left photographing lenses are moved toward the directions to approach each other by the shifting amount Sl accompanying a decrease in the distance L to the subject that is focused, the loci of motion of main points of the photographing lenses describe a loose curve, and the visual fields of the right and left photographing lenses at the focal distance are brought into agreement at all times.
The conventional mechanism for automatically adjusting the distance between the optical axes is so constituted that the main points of the photographing lenses move on loci given by the above-mentioned formula by using a cam, a guide and the like, and that the focal point is adjusted being interlocked to the adjustment of the distance between the optical axes. In practice, however, a satisfactory effect for correcting the distance between the optical axes is not obtained in many cases.
This problem is caused by the fact that all subjects in the picture seldom exist at a focal distance and, in many cases, the subjects are existing at various distances. For example, when a scenery is to be photographed by bringing the focal point to infinity, some material bodies are in many cases photographed in front of the subject at infinity. In taking a picture from a close distance, e.g., in shooting flowers in a flower garden from an upper tilted direction, the picture includes flowers in front of the flowers at the central portion of the picture to where the focal point is adjusted. When a front portrait is to be shot by adjusting the focal point to the eyes of a human model, the nose of the model is, then, located in front of the focal distance.
In a stereo slide in which the subject that strongly affects the matching of the right and left images exists at a distance closer than the subject at the focal distance, the stereo image of the subject at the closer distance is formed in front of the stereo windows and appears unnatural. To correct this, it becomes necessary to mask the outer side edges of the right and left pictures when the films are to be mounted in the same manner as in the prior art and to correct the perspective feeling by adjusting the pitch for mounting the right and left films. Thus, the action of the conventional mechanism for automatically adjusting the distance between the optical axes is never perfect.
Therefore, a technical problem must be solved in order to provide a stereo camera having a practicable function for adjusting the distance between the optical axes so that stereo pictures featuring an optimum stereo effect can be easily shot by anybody. The object of the present invention is to solve this problem.
The present invention is proposed in order to achieve the above-mentioned object, and provides a stereo camera provided with a mechanism for automatically adjusting the distance between the optical axes, in which two photographing lenses are mounted on independent lens boards, the distance between the right and left lens boards is changed being interlocked to the back-and-forth motion of the lens boards accompanying the operation for adjusting the focal point, and the distance between the optical axes of the two photographing lenses is corrected depending upon the focal distance, wherein the loci of motion of the two photographing lenses are right-and-left symmetrical straight lines connecting the positions at where the distance between the optical axes of the two photographing lenses at a position for adjusting the focal point to infinity is narrower than a pitch between the right and left exposed pictures or, preferably, connecting the positions within a range of distance between the optical axes in which the visual fields of the two photographing lenses are brought into agreement at a distance of 2 to 3 meters in front of the main points of the photographing lenses along the optical axes, to the positions of the distance between the optical axes at where the visual fields of the two photographing lenses at a position for adjusting the shortest focal point are brought into agreement at a focal distance, or to the positions in the vicinities thereof.
The invention further provides a stereo camera in which the loci of motion of the two photographing lenses are right-and-left symmetrical arcs passing through the positions at where the distance between the optical axes of the two photographing lenses at a position for adjusting the focal point to infinity is narrower than a pitch between the right and left exposed pictures or, preferably, through the positions within a range of distance between the optical axes in which the visual fields of the two photographing lenses are brought into agreement at a distance of 2 to 3 meters in front of the main points of the photographing lenses along the optical axes, and through the positions of the distance between the optical axes at where the visual fields of the two photographing lenses at a position for adjusting the shortest focal point are brought into agreement at a focal distance or through the positions at where the distance between the optical axes is slightly narrower than the distance between the optical axes with which the visual fields are in agreement at the focal distance.